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Elusive Solar Light-Trapping Limit Nearly Reached

Photonics.comFeb 2014
DELFT, Netherlands, Feb. 27, 2014 — The theoretical limit of light-trapping in solar cells has eluded researchers for decades. But a group from Delft University of Technology (TU Delft) has come closer to it than anyone else.

The researchers, members of TU Delft’s Photovoltaic Materials and Devices (PVMD) group, have experimentally demonstrated the theoretical limit of the enhancement of light absorption using an advanced metal-free light-trapping scheme for the ultrathin crystalline silicon wafers that they developed.

A group in the Netherlands has nearly reached the theoretical limit of light absorption in solar cells, which has eluded researchers for decades. Courtesy of ACS Photonics.
On the front of the silicon wafers, they applied a nanotexture known as black silicon. On the back, they implemented a random pyramidal texture coated with a photonic dielectric back reflector, designed to exhibit maximal and omnidirectional internal reflectance.

Wafers thinner than 35 µm allowed the group to achieve more than 99 percent of the theoretical classical light absorption limit in the 400- to 1200-nm spectral range (with the photonic reflector), and up to 99.8 percent with the silver back reflector.

Successful implementation of the light-trapping scheme in crystalline silicon solar cells required an adequate surface passivation of the front nanotexture.

The theoretical limit of light absorption in solar cells is near. Courtesy of Steve Rainwater.
For this purpose, the researchers also developed thermal silicon oxide and aluminum oxide passivation layers.

These developments essentially pave the way for the next generation of high-efficiency, cost-effective ultrathin crystalline silicon solar cells, the researchers said.

The work was funded by Agentschap NL, with project partners Solland Solar Cells and the Energy Research Centre of the Netherlands. The research is published in ACS Photonics (doi: 10.1021/ph4001586).

The ratio of reflected flux to incident flux. Unless otherwise specified, the total reflectance is meant; it is sometimes convenient to divide this into the sum of the specular and the diffuse reflectance.